Formation of finfet junction

ABSTRACT

A finFET structure, and method of forming such structure, in which a germanium enriched nanowire is located in the channel region of the FET, while simultaneously having silicon-germanium fin in the source/drain region of the finFET.

BACKGROUND

The present invention relates to semiconductor devices, and particularlyto forming source/drain regions, and forming abrupt Fin Field EffectTransistor (FinFET) junctions.

Field effect transistors (FETs) are commonly employed in electroniccircuit applications. FETs may include a source region and a drainregion spaced apart by a semiconductor channel region. A gate,potentially including a gate dielectric layer, a work function metallayer, and a metal electrode, may be formed above the channel region. Byapplying voltage to the gate, the conductivity of the channel region mayincrease and allow current to flow from the source region to the drainregion.

FinFETs are an emerging technology which may provide solutions to fieldeffect transistor (FET) scaling problems at, and below, the 22 nm node.FinFET structures may include at least a narrow semiconductor fin gatedon at least two sides of each of the semiconductor fin, as well as asource region and a drain region adjacent to the fin on opposite sidesof the gate. FinFET structures having n-type source and drain regionsmay be referred to as nFinFETs, and FinFET structures having p-typesource and drain regions may be referred to as pFinFETs.

In some FinFET structures, different materials may be used for the finsof pFinFETs and nFinFETs in order to improve device performance.However, a material that may improve pFinFET performance may reduce nFETperformance, and vice versa. For example, while pFinFET performance maybe improved by forming fins made of silicon-germanium, nFinFETperformance may instead be improved by forming fins made of undoped orcarbon-doped silicon and may be degraded by forming fins made ofsilicon-germanium. Further, pFinFETs and nFinFETs are often fabricatedon the same substrate.

BRIEF SUMMARY

An embodiment of the invention may include a method for forming a finFETstructure. The finFET structure contains a silicon germanium fin havinga source/drain region and a channel region, an epitaxial layer locatedon the source/drain region of the silicon germanium fin, a dummy gatelocated above the channel region of the silicon germanium fin, and aspacer located between the dummy gate and the epitaxial layer and abovethe source/drain region of the fin. The dummy gate is removed. A thermalcondensation is performed on an exterior portion of the silicongermanium fin in the channel region. The thermal condensation forms asilicon oxide layer on the exterior portion of the silicon germanium finin the channel region and an enriched germanium fin on an interiorportion of the silicon germanium fin in the channel region. The siliconoxide layer is removed from the exterior portion of the silicongermanium fin.

An additional embodiment of the invention may include a semiconductorstructure containing a fin. The fin contains a source/drain region and achannel region. A portion of the fin in the source/drain region issilicon germanium, and the portion of the fin in the channel regioncontains a higher concentration of germanium than the source drainregion. An epitaxial layer may be located above the source/drain region.A spacer layer may be located above the source/drain region and adjacentto the epitaxial layer, wherein the surface of the spacer layer oppositethe epitaxial layer abuts the channel region.

An additional embodiment of the invention may include a semiconductorstructure containing a fin. The fin contains a source/drain region and achannel region. A portion of the fin in the source/drain region issilicon germanium, and the cross-sectional area of the portion of thefin in the source/drain region is greater than the cross-sectional areaof the portion of the fin in the channel region. An epitaxial layer maybe located above the source/drain region. A spacer layer may be locatedabove the source/drain region and adjacent to the epitaxial layer,wherein the surface of the spacer layer opposite the epitaxial layerabuts the channel region.

BRIEF DESCRIPTION OF THE SEVERAL DRAWINGS

FIG. 1A is a top view of a FinFET device with a dummy gate, according toan example embodiment;

FIG. 1B is a cross sectional view along a-a of FIG. 1A

of a FinFET device with a dummy gate, according to an exampleembodiment;

FIG. 1C is a cross sectional view along b-b of FIG. 1A of a FinFETdevice with a dummy gate, according to an example embodiment;

FIG. 2A is a top view of a FinFET device after removing the dummy gate,according to an example embodiment;

FIG. 2B is a cross sectional view along a-a of FIG. 2A of a FinFETdevice after removing the dummy gate, according to an exampleembodiment;

FIG. 3A is a top view of a FinFET device following thermal condensationof the exposed fin, according to an example embodiment;

FIG. 3B is a cross sectional view along a-a of FIG. 3A of a FinFETdevice following thermal condensation of the exposed fin, according toan example embodiment;

FIG. 3C is a cross sectional view along b-b of FIG. 3A of a FinFETdevice following thermal condensation of the exposed fin, according toan example embodiment;

FIG. 3D is a cross sectional view along c-c of FIG. 3B of a FinFETdevice following thermal condensation of the exposed fin, according toan example embodiment;

FIG. 4A is a top view of a FinFET device following the removal of thesilicon oxide layer formed by thermal condensation, according to anexample embodiment;

FIG. 4B is a cross sectional view along a-a of FIG. 4A of a FinFETdevice following the removal of the silicon oxide layer formed bythermal condensation, according to an example embodiment;

FIG. 4C is a cross sectional view along b-b of FIG. 4A of a FinFETdevice following the removal of the silicon oxide layer formed bythermal condensation, according to an example embodiment;

FIG. 4D is a cross sectional view along c-c of FIG. 4B of a FinFETdevice following the removal of the silicon oxide layer formed bythermal condensation, according to an example embodiment; and

FIG. 5 is a cross sectional view of a FinFET device following depositionof a replacement metal gate, according to an exemplary embodiment.

Elements of the figures are not necessarily to scale and are notintended to portray specific parameters of the invention. For clarityand ease of illustration, dimensions of elements may be exaggerated. Thedetailed description should be consulted for accurate dimensions. Thedrawings are intended to depict only typical embodiments of theinvention, and therefore should not be considered as limiting the scopeof the invention. In the drawings, like numbering represents likeelements.

DETAILED DESCRIPTION

Example embodiments now will be described more fully herein withreference to the accompanying drawings, in which example embodiments areshown. This disclosure may, however, be embodied in many different formsand should not be construed as limited to the example embodiments setforth herein. Rather, these example embodiments are provided so thatthis disclosure will be thorough and complete and will fully convey thescope of this disclosure to those skilled in the art. In thedescription, details of well-known features and techniques may beomitted to avoid unnecessarily obscuring the presented embodiments.

For purposes of the description hereinafter, terms such as “upper”,“lower”, “right”, “left”, “vertical”, “horizontal”, “top”, “bottom”, andderivatives thereof shall relate to the disclosed structures andmethods, as oriented in the drawing figures. Terms such as “above”,“overlying”, “atop”, “on top”, “positioned on” or “positioned atop” meanthat a first element, such as a first structure, is present on a secondelement, such as a second structure, wherein intervening elements, suchas an interface structure may be present between the first element andthe second element. The term “direct contact” means that a firstelement, such as a first structure, and a second element, such as asecond structure, are connected without any intermediary conducting,insulating or semiconductor layers at the interface of the two elements.

In the interest of not obscuring the presentation of embodiments of thepresent invention, in the following detailed description, someprocessing steps or operations that are known in the art may have beencombined together for presentation and for illustration purposes and insome instances may have not been described in detail. In otherinstances, some processing steps or operations that are known in the artmay not be described at all. It should be understood that the followingdescription is rather focused on the distinctive features or elements ofvarious embodiments of the present invention.

Forming FinFET devices where the channel region and source/drain regionof the fin have different material properties may allow forindependently tuning each region, which may increase the resultingdevice performance of the overall structure. Manipulation of the channelregion may be performed in order to change the characteristics of thematerial used and improve the overall characteristics of the device.Such a strategy may be performed following the removal of a dummy gateduring the manufacturing of a replacement metal gate and use a techniquesuch as thermal condensation to drive silicon out of a channel region ofthe FinFET device, thereby increasing the germanium concentration in thechannel region of a silicon germanium fin.

Referring to FIGS. 1A-1C, a dummy gate 10 may be located above asubstrate 100. The dummy gate 10 may contain a fin 110 located above asubstrate 100. The fin 110 may have a width, W₁, ranging fromapproximately 2 nm to approximately 40 nm, preferably approximately 4 nmto approximately 20 nm; a height, H₁, ranging from approximately 5 nm toapproximately 300 nm, preferably approximately 10 nm to approximately 80nm; and a cross-sectional area, A₁, ranging from approximately 10 nm² toapproximately 12000 nm², preferably approximately 40 nm² toapproximately 1600 nm². The fin 110 may be formed, for example byremoving material from the substrate 100 using a photolithographyprocess followed by an anisotropic etching process such as reactive ionetching (RIE) or plasma etching. Other methods of forming fins known inthe art may also be utilized, such as sidewall image transfer (SIT).

In some embodiments, the substrate 100 may be a semiconductor oninsulator (SOI) substrate. In embodiments where the substrate 100 is anSOI substrate, the fins 110 may be formed from a top semiconductor layerseparated from a base semiconductor substrate by a buried insulatorlayer (not shown). In such embodiments, the top semiconductor layer andthe base semiconductor substrate may be made be made of anysemiconductor material typically known in the art, including, forexample, silicon, germanium, silicon-germanium alloy, silicon carbide,silicon-germanium carbide alloy, and compound (e.g. II-VI) semiconductormaterials. In such embodiments, the fin 110 may be electricallyinsulated from other structures formed on the device by removing thesemiconductor material adjacent to the fin. The buried insulator layermay have a thickness ranging from approximately 20 to approximately 500nm, preferably about 150 nm. In such embodiments, the fin 110 may reston the buried insulator layer, separated from the base semiconductorsubstrate. In a preferred embodiment, the fin 110 may be silicongermanium, having a formula of Si_(1-x)Ge_(x), whereby the concentrationof germanium, x, may be from about 0.2 to about 0.5.

Still referring to FIGS. 1A-1C, a dummy gate 10 may be located above thesubstrate 100, and cross over a channel region of the fin 110. The dummygate 10 may be substantially perpendicular to the fin 110, where the fin110 passes through the dummy gate 10 in a gate region, and asource/drain region of the fin 110 may be located on both sides of thegate region. The dummy gate 10 may have a height of approximately 40 nmto approximately 200 nm, preferably approximately 50 nm to approximately150 nm. The dummy gate 10 may include a sacrificial gate structure 140,which may include a dummy gate dielectric (not shown), a dummy gatematerial (not shown) and a hardmask (not shown), that may be laterremoved and replaced by a replacement gate dielectric, WF metal and areplacement gate electrode. In an example embodiment, the dummy gatematerial may be made of a polysilicon material. In an exampleembodiment, the dummy gate dielectric (e.g., silicon oxide) formed usingknown deposition techniques known in the art, including, for example,ALD, CVD, PVD, MBD, PLD, LSMCD, sputtering, and plating. In someembodiments, the hardmask may be made of an insulating material, suchas, for example, silicon nitride or silicon oxide, capable of protectingthe sacrificial gate structure 140 during subsequent processing steps.Further, while only a single dummy gate 10 is shown, some embodimentsmay include more than one gate above the fin 110.

Still referring to FIGS. 1A-1C, a spacer 130 may be formed adjacent tothe exposed vertical surfaces of the sacrificial gate structure 140 andcover a portion of the substrate 100 and the fin 110. The spacer 130 maybe made of any suitable insulating material, such as silicon nitride,silicon oxide, silicon oxynitrides, or a combination thereof, and mayhave a thickness ranging from 2 nm to approximately 100 nm. The spacer130 may be formed by any method known in the art, including depositing aconformal insulating layer over the gate structure 120 andanisotropically etching the material from the horizontal surfaces.Further, in various embodiments, the spacer 130 may include one or morelayers.

Still referring to FIGS. 1A-1C, a source/drain epitaxy 150 is grown on asource/drain region of the fin 110. The source/drain epitaxy 150 mayinclude a semiconductor material epitaxially grown on the fin. In someembodiments, a semiconductor material may be epitaxially grown on theexisting crystal lattice of the fin 110. In an example embodiment, thesemiconductor material may be silicon-germanium. In such an embodiment,the semiconductor material may contain, for example, approximately 20%to approximately 100% germanium, approximately 0% to approximately 80%silicon, and may be doped with p-type dopants such as boron inconcentrations ranging from approximately 1×10²⁰ atoms/cm³ toapproximately 2×10²¹ atoms/cm³.

The terms “epitaxial growth and/or deposition” and “epitaxially formedand/or grown” mean the growth of a semiconductor material on adeposition surface of a semiconductor material, in which thesemiconductor material being grown may have the same crystallinecharacteristics as the semiconductor material of the deposition surface.In an epitaxial deposition process, the chemical reactants provided bythe source gases are controlled and the system parameters are set sothat the depositing atoms arrive at the deposition surface of thesemiconductor substrate with sufficient energy to move around on thesurface and orient themselves to the crystal arrangement of the atoms ofthe deposition surface. Therefore, an epitaxial semiconductor materialmay have the same crystalline characteristics as the deposition surfaceon which it may be formed. For example, an epitaxial semiconductormaterial deposited on a {100} crystal surface may take on a {100}orientation. In some embodiments, epitaxial growth and/or depositionprocesses may be selective to forming on semiconductor surfaces, and maynot deposit material on dielectric surfaces, such as silicon dioxide orsilicon nitride surfaces.

Still referring to FIGS. 1A-1C, an inter layer dielectric 160(hereinafter “ILD 160”) may be deposited above the source/drain epitaxy150. The ILD 160 may include any suitable dielectric material, forexample, silicon oxide, silicon nitride, hydrogenated silicon carbonoxide, silicon based low-k dielectrics, or porous dielectrics. Knownsuitable deposition techniques, such as, for example, atomic layerdeposition (ALD), chemical vapor deposition (CVD), plasma enhancedchemical vapor deposition, spin on deposition, or physical vapordeposition (PVD) may be used to form the ILD 160. The ILD 160 may eachhave a thickness ranging from approximately 100 nm to approximately 150nm and ranges there between.

Referring to FIGS. 2A-2B, the sacrificial gate structure 140 may beremoved, creating a gate void 145. The gate void may be defined as theempty space between spacers 130, and above the substrate 100 and the fin110. The sacrificial gate structure 140 may be removed by selectivelyetching the dummy gate using an isotropic or an anisotropic etchingprocess such as, for example, reactive ion etching (RIE), wet etching orplasma etching (not shown). The chemicals and processes selected for theetch should be selected such that the dummy gate is removed, while thespacer 130, ILD 160 and fin 110 remain substantially unaffected.

Referring to FIGS. 3A-3D, thermal condensation of the exposed fin 110may be performed. The thermal condensation includes oxidation of anouter region of the fin 110 in the channel region, which may causegermanium to migrate toward the center of the fin 110, forming agermanium enriched channel region 200 and an oxidized channel region210. The thermal condensation process selectively oxidizes the siliconof the silicon germanium fin to silicon oxide, driving the germaniumtowards the inner part of the fin, and subsequently increasing theconcentration of germanium in the non-oxidized portions of the fin 110.Conversely, the migration/diffusion of germanium out of the oxidizedregion causes silicon to migrate/diffuse into the oxidized region duringcondensation, further increasing the germanium concentration in 210.Following thermal condensation, the enriched channel region 200 has achemical formula of Si_(1-y)Ge_(y), whereby the concentration ofgermanium, y, may be from about 0.9 to about 1.

Additionally, during thermal condensation, dopants located in thesource/drain epitaxy 150 may migrate into the fin 110, creating a dopedsource/drain region 115. The dopant migration may be impeded by the highconcentration of germanium in the germanium enriched channel region 200,and thus may not be present in the germanium enriched channel region200. Thus, an abrupt junction may be formed between the dopedsource/drain region 115 and the germanium enriched channel region 200due to the diffusion of dopants from the source/drain epitaxy 150, andthe thermal condensation process. In a preferred embodiment, the dopedsource/drain region 115 may contain dopants such as boron inconcentrations ranging from approximately 1×10²⁰ atoms/cm³ toapproximately 1×10²¹ atoms/cm³.

Following the thermal condensation, the germanium enriched channelregion has a resulting height, H₂, width, W₂, and cross-sectional area,A₂, which are all less than the height, H₁, width, W₁, andcross-sectional area, A₁, of the fin 110 and doped source/drain region115. In an example embodiment, thermal condensation may be performed inorder to create a germanium enriched channel region 200 containing pure,or substantially pure, germanium. The terms pure and substantially purerefer to a content of at least 90 mole % germanium, more preferably atleast 95 mole % germanium.

By “germanium enriched” it is meant a semiconductor material in whichgermanium is present in a higher concentration than the original silicongermanium fin (i.e. y>x). In some embodiments, the diffusion ofgermanium creates a germanium enriched channel region 200 in which thegermanium is pure, or substantially pure. This may be the result ofmigration of the germanium atoms to the center of the fin 110.

The thermal condensation of the present application is a thermaloxidation process that is performed at temperature sufficient enough tooxidize the external region of the fin 11 and cause diffusion ofgermanium to the germanium enriched channel region 200 from the oxidizedchannel region 210. In one embodiment of the present application, thethermal condensation is performed at a temperature from 700° C. to 1300°C. In another embodiment of the present application, the thermalcondensation is performed at a temperature from 900° C. to 1200° C.

Moreover, the thermal condensation of the present application isperformed in an oxidizing ambient which includes at least oneoxygen-containing gas such as O₂, NO, N₂O, ozone, air and other likeoxygen-containing gases. The oxygen-containing gas may be admixed witheach other (such as an admixture of O₂ and NO), or the gas may bediluted with an inert gas such as He, Ar, N₂, Xe, Kr, or Ne.

The thermal condensation process of the present application may becarried out for a variable period of time. In one example, the thermalcondensation process is carried out for a time period from 5 seconds toabout 5 hours, depending on thermal oxidation temperature and oxidationspecies. In another embodiment, the thermal condensation process may becarried out for a time period from 5 minutes to about 30 minutes. Thethermal condensation process of the present application may be carriedout at a single targeted temperature, or various ramp and soak cyclesusing various ramp rates and soak times can be employed.

Referring to FIGS. 4A-4D, the oxidized channel region 210 may beremoved, leaving the germanium enriched channel region 200 as thecontact between the doped source/drain region 115 on either side of thegate structure. Removal of the oxidized channel region 210 may beperformed by selectively etching the oxidized channel region 210, whilemaintaining the germanium enriched channel region 200. This may beperformed using etching techniques known in the art such as, forexample, RIE, wet etching or plasma etching.

Following the removal of the oxidized channel region 210, the structurethat results may be a fin having a channel region, with a source/drainregion on located on each side of the channel region. In someembodiments, more than 1 channel region, and more than 2 source/drainregions, may be contained on a single fin. The channel region may be agermanium enriched channel region 200, where the concentration ofgermanium in the channel region is higher than the concentration ofgermanium located in the original silicon germanium fin 110, and/or thedoped source/drain region 115. The doped source/drain region 115 maycontain dopants that migrate from the source/drain epitaxy 150 duringthe thermal condensation process, thereby increasing the concentrationof the dopants as compared to the original silicon germanium fin 110.Additionally, the resulting germanium enriched channel region 200 mayhave a smaller cross-sectional area A₂ than the cross-sectional area A₁of the original fin 110, or the doped source/drain region 115. This maybe due to thermal condensation concentrating the germanium of theoriginal fin 110 into the center of the fin, and then removing theunwanted silicon oxide of the oxidized channel region, during theformation of the enriched silicon germanium channel region.

Referring to FIG. 5 a replacement metal gate (i.e. a replacement gatedielectric 300 and a replacement gate electrode 310) may be created inthe gate void 145. The replacement gate dielectric 300 may be depositedfirst. In one embodiment, the replacement gate dielectric 300 mayinclude silicon oxide (Si_(x)O_(y)) or a high-k oxide such as, forexample, hafnium oxide (Hf_(x)O_(y)), zirconium oxide (Zr_(x)O_(y)),aluminum oxide (Al_(x)O_(y)), titanium oxide (Ti_(x)O_(y)), lanthanumoxide (La_(x)O_(y)), strontium titanium oxide (Sr_(x)Ti_(y)O_(z)),lanthanum aluminum oxide (La_(x)Al_(y)O_(z)), and mixtures thereof. Thereplacement gate dielectric 300 may be deposited over the fin 110 usingany suitable deposition technique known the art, including, for example,atomic layer deposition (ALD), chemical vapor deposition (CVD), physicalvapor deposition (PVD), molecular beam deposition (MBD), pulsed laserdeposition (PLD), or liquid source misted chemical deposition (LSMCD).

Following the deposition of the replacement gate dielectric 300, in someembodiments a work function metal layer may be deposited. The workfunction metal layer may include, for example, aluminum, lanthanumoxide, magnesium oxide, strontium titanate, strontium oxide, TiN, TaN.The work function metal layer may be formed using any suitable metaldeposition technique, including, for example, CVD, PVD, and ALD,sputtering, and plating.

In some embodiments, a high temperature anneal may be performed prior tothe deposition of the gate electrode. The high temperature anneal may beperformed in order to increase the performance of the replacement metalgate stack. The high temperature anneal may be performed at temperaturesranging from approximately 600° Celsius to approximately 1250° Celsiusand may be annealed for approximately 0.1 to approximately 30 second. Insome embodiments, the annealing temperature may be substantially uniformthroughout the annealing period, however in other embodiments theannealing period include one or more ramping cycles where thetemperature is decreased or increased. Following the anneal, additionalwork function metal layers, dielectric layer or any other layers knownin the art may be deposited.

A replacement gate electrode 310 may be deposited above the replacementgate dielectric 300 or work function layer. The replacement gateelectrode 310 may be made of gate conductor materials including, but notlimited to, zirconium, tungsten, tantalum, hafnium, titanium, aluminum,ruthenium, metal carbides, metal nitrides, transition metal aluminides,tantalum carbide, titanium carbide, tantalum magnesium carbide, orcombinations thereof. The replacement gate electrode 310 may be formedusing any suitable metal deposition technique, including, for example,CVD, PVD, and ALD, sputtering, and plating.

The descriptions of the various embodiments of the present inventionhave been presented for purposes of illustration but are not intended tobe exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to best explain theprinciples of the embodiment, the practical application or technicalimprovement over technologies found in the marketplace, or to enableother of ordinary skill in the art to understand the embodimentsdisclosed herein. It is therefore intended that the present inventionnot be limited to the exact forms and details described and illustratedbut fall within the scope of the appended claims.

What is claimed is:
 1. A finFET structure comprising: a fin, wherein thefin comprises a source/drain region and a channel region, wherein aportion of the fin in the source/drain region is silicon germanium; anepitaxial layer located above the source/drain region; a spacer layerlocated above the source/drain region and adjacent to the epitaxiallayer; and a dielectric layer surrounding the channel region of the fin,wherein a first portion of a vertical surface of the dielectric layer isin direct contact with the spacer layer and above the channel region ofthe fin, wherein a second portion of the vertical surface of thedielectric layer is in direct contact with the source/drain region ofthe fin, and wherein a horizontal surface of the dielectric layer is indirect contact with the entire channel region.
 2. The structure of claim1, wherein the concentration of germanium in the portion of the fin inthe channel region is greater than 90 mole %.
 3. The structure of claim1, wherein the epitaxial layer comprises boron.
 4. The structure ofclaim 1, wherein the portion of the fin in the source/drain regionfurther comprises boron.
 5. The structure of claim 1, wherein thedielectric layer is a high-k dielectric.
 6. The structure of claim 1,wherein the second portion of the vertical surface is above the channelregion of the fin.
 7. The structure of claim 1, wherein the secondportion of the vertical surface is adjacent to the channel region of thefin.